EDMUND GUNTER (1581-1626), English mathematician, of Welsh extraction, was born in Hertfordshire in 1581. He was educated at Westminster school, and in 1599 was elected a student of Christ Church, Oxford. He took orders, became a preacher in 1614, and in 1615 proceeded to the degree of bachelor in divinity. Mathematics, however, which had been his favourite study in youth, continued to engross his attention, and on the 6th of March 1619 he was appointed professor of astronomy in Gresham College, London. This post he held till his death on the loth of December 1626. With Gunter's name are associated several useful inventions, descriptions of which are given in his treatises on the Sector, Cross-staff, Bow, Quadrant and other Instruments. He contrived his sector about the year 16o6, and wrote a description of it in Latin, but it was more than sixteen years afterwards before he allowed the book to appear in English. In 162o he published his Canon triangulorum (see LOGARITHMS). There is reason to believe that Gunter was the first to discover (in 1622 or 1625) that the magnetic needle does not retain the same declination in the same place at all times. By desire of
James I. he published in 1624 The Description and Use of His Majestie's Dials in Whitehall Garden, the only one of his works which has not been reprinted. He introduced the words cosine and cotangent, and he suggested to Henry Briggs, his friend and colleague, the use of the arithmetical complement (see Brigg's Arithmetica Logarithmica, cap. xv.). His practical inventions are briefly noticed below:
Gunter's Chain, the chain in common use for surveying, is 22 yds. long and is divided into too links. Its usefulness arises from its decimal or centesimal division, and the fact that 10 square chains make an acre.
Gunter's Line, a logarithmic line, usually laid down upon scales, sectors, &c. It is also called the line of lines and the line of numbers, being only the logarithms graduated upon a ruler, which therefore serves to solve problems instrumentally in the same manner as logarithms do arithmetically.
Gunter's Quadrant, an instrument made of wood, brass or other substance, containing a kind of stereographic projection of the sphere on the plane of the equinoctial, the eye being supposed to be placed in one of the poles, so that the tropic, ecliptic, and horizon form the arcs of circles, but the hour circles are other curves, drawn by means of several altitudes of the sun for some particular latitude every year. This instrument is used to find the hour of the day, the sun's azimuth, &c., and other common problems of the sphere or globe, and also to take the altitude of an object in degrees.
Gunter's Scale (generally called by seamen the Gunter) is a large plane scale, usually 2 ft. long by about 12 in. broad, and engraved with various lines of numbers. On one side are placed the natural lines (as the line of chords, the line of sines, tangents, rhumbs, &c.), and on the other side the corresponding artificial or logarithmic ones. By means of this instrument questions in navigation, trigonometry, &c., are solved with the aid of a pair of compasses.